4f binding-energy shifts of the light-actinide dioxides and tetrafluorides

With our measurements of the 4f binding energies of NpF4 and PuF4, values for all the light-actinide dioxides and tetrafluorides (Th--Pu, except Pa) are available. In spite of the fact that the electronegativities of these elements are nearly constant, the chemical shifts for each series show a regular increase, relative to the metals. Using the results of previously reported band-structure and molecular-orbital calculations, we show that the shifts result from increasing differences in 5f occupation and, to a lesser extent, increases in the 5f--core-level Coulombic interaction. Recently reported L3 x-ray-absorption and renormalized-atom calculations are employed to assess the importance of final-state screening energies in both the metals and the insulating compounds